i 6 



Bulletin 2 

Structural Materials Research Laboratory 

Lewis Institute 

Chicago 



Effect of Curing Condition on 

the Wear and Strength 

of Concrete 



By 



DUFF A. ABRAMS 

M 

Professor in Charge of Laboratory 



Published by the 

STRUCTURAL MATERIALS RESEARCH LABORATORY 

Lewis Institute 

Chicago 

MAY, 1919 







\^ 






v v 



"O ESEARCHES in the properties of concrete and concrete materials 
-*-^ at the Structural Materials Research Laboratory are being carried 
out through the cooperation of the Lewis Institute and the Portland 
Cement Association, Chicago. The research work has been under way 
since September 1, 1914. 

The control of the policies of the Laboratory is vested in an Advisory 
Committee, consisting of representatives of the Lewis Institute and the 
Portland Cement Association as follows: 

Lewis Institute: 

DUFF A. ABRAMS, Professor in charge of Laboratory 
PHILIP B. WOODWORTH, Professor of Engineering 

Portland Cement Association: 

F. W. KELLEY, Chairman Technical Problems Committee, Albany, N. Y. 
ERNEST ASHTON, Member') technical Problems Committee, Allentown, 
Pa. 

The investigations are being carried out by a staff of engineers, 
chemists, and assistants who give their entire time to this 'work. The 
results of these researches are published in the form of papers before 
engineering and technical societies and in Circulars and Bulletins issued 
by the Laboratory. 






v^5 EFFECT OF CURING CONDITION ON THE WEAR AND 

O STRENGTH OF CONCRETE* 

By Duff A. Abrams. 
Introduction. 

The necessity for careful restriction on the quantity of mixing water 
used in concrete, and the importance of proper curing conditions during 
the period of setting and hardening are not generally appreciated by 
engineers and contractors doing concrete work. In view of the wide- 
spread use of concrete in the construction of pavements, floors, loading 
platforms, and in other places requiring high strength and resistance to 
abrasion, it seemed desirable to carry out an experimental study which 
would bring out the effect of water content and curing conditions on 
the compressive strength and the wearing resistance of concrete, and the 
relation between these two properties. 

These tests were made as a part of the experimental studies of the 
properties of concrete and concrete materials, being carried out through 
the co-operation of Lewis Institute and the Portland Cement Association 
at the Structural Materials Research Laboratory, Lewis Institute, Chicago. 

This series comprised compression tests of 120 6 x 12-inch cylin- 
ders and wear tests on 300 blocks, 8 inches square and 5 inches in thick- 
ness. A 1-4 mix was used throughout, that is, 1 volume cement and 4 
volumes mixed aggregate. This mix is about the same as the l-V/ 2 -3 or 
1-2-3 mixes generally used for concrete which is to withstand high stresses 
or to form the wearing surface of pavements. Most of the tests were 
made on sand and pebble aggregates. One group was repeated with 
crushed limestone as coarse aggregate. 

Concrete of six different consistencies was used, each being stored 
under four different conditions : 

(1) Damp sand 4 months, tested damp. 

(2) Damp sand 21 days, air 99 days. 

(3) Damp sand 3 days, air 117 days. 

(4) Air of laboratory for entire curing period of 4 months. 

Parallel tests were made throughout on compression and wear. All 
tests were made at the age of 4 months. 

The wear blocks were tested in the Talbot-Jpnes rattler by the same 
methods that were used in other tests carried out in this laboratory.f 

♦Authorized reprint from the report of the Committee on Masonry of 
the American Railway Engineering Association, Proc, Vol. 20, 1919. 

tSee "A Method of Making Weai^Tests of Concrete" by D. A. Abrams, 
Proc. American Society for Testing Materials, Part IT. 1916; also "Effect of 
Time of Mixing on the Strength and Wear of Concrete." by P. A. Abrams, 
Proc. American Concrete Institute, 1918. 

1 



2 Structural Materials Research Laboratory 

Acknowledgment is due to the Chicago Gravel Company, Chicago, 
for their courtesy in furnishing the sand and pebble aggregate used in 
these tests, and to Dolese & Shepard, Chicago, for the crushed limestone. 

Materials. 

The Portland cement used in these tests consisted of a mixture of 
equal parts of four brands purchased in the Chicago market. The brands 
were thoroughly mixed by placing one sack of each in a concrete mixer 
and running for about one minute. Complete tests of the cement are 
given in Table 1. 

Table 1 — Tests of Cement. 

The cement consisted of a mixture of equal parts of four brands purchased on the Chicago 
market (Lot No. 3705). 

All tests made in accordance with standard methods of the American Society for Testing 
Materials. 

Miscellaneous Tests. 





Normal 

Consistency 

Per Cent 

by Weight 


Time of Setting 




Fineness 
Residue 


Vicat Needle 


Gillmore Needle 


Soundness 
Test (over 


on 200 

Sieve 


Initial 


Final 


Initial 


Final 


Boiling 
Water) 




h. m. 


h. m. 


h. m. 


h. m. 




20.4 


23.0 


4.25 


8.05 


5.10 


8.45 


O.K, 



Mortar Strength Tests. 



1-3 standard sand mortar. 



Mixing 
Water 
Percent 


Briquets 
Tensile Strength — lb. per sq. in. 


2 by 4-in. Cylinders 
Compressive Strength — lb. per sq. in. 


7 Da. 


28 Da. 


3 Mo. 


6 Mo. 


1 Yr. 


2 Yr. 


7 Da. 


28 Da. 


3 Mo. 


6 Mo. 


lYr. 


2Yr. 


10.3 


266 


367 


464 


431 


415 


357 


2080 


3800 


4240 


5130 


5060 


4600 



The aggregates consisted of sand and pebbles from the Chicago 
Gravel Company's plant near Elgin, 111., and crushed limestone from 
Dolese & Shepard Company's quarry. Before using, the sand was screened 
through a No. 4 sieve. All material coarser than this size was rejected. 
The sand was used without further screening, but care was taken to see 
that the material in the bin was thoroughly mixed so that it was uniform 
throughout the series. Pebbles and crushed limestone were screened to 
three different sizes (No. 4-^, H~ 3 A, and 24-1/4 inches) and recombined 
in definite proportions for each batch, as shown by the sieve analyses in 
Table 2. 



Wear and Strength of Concrete 3 

The water was from the city water supply obtained from Lake Mich- 
igan. 

The weights per cubic foot of aggregates were determined by means 
of machined, cast-iron measures having capacities of Vs and l / 2 cubic foot. 
The Ys cubic foot measure was used for the sand and the l / 2 cubic foot 
for the coarse aggregates and the mixed aggregates. The inside diameter 
of each measure is equal to the depth. The test was made by filling the 
measure about one-third full and puddling with a 5^-inch steel bar pointed 
at the lower end. Filling and puddling were continued in like manner 
until the measure was full. After striking off with a straight-edge the 
weight was determined. This is the method recommended by Committee 
C-9 on Concrete of the American Society for Testing Materials, but the 
method has not yet been standardized by the Society. 



Table 2 — Sieve Analysis of Aggregates. 

Sieves manufactured by the W. S. Tyler Company, Cleveland, Ohio. 



Sieve 

Number 

or 

Size 


Size of 

Clear 

Opening 

inches 


Per Cent, by Weight Coarser than Each Sieve 


Sand 


Pebbles 


Crushed 
Limestone 


Sand 

and 

Pebbles 


Sand 

and 

Limestone 


100 
48 
28 
14 
8 
4 

H 


.0058 
0116 
023 
046 
093 
185 

.37 

.75 
1 25 


98 
90 
60 
42 
22 



100 
100 
100 
100 
100 
100 
84 
50 



100 
100 
100 
100 
100 
100 
84 
50 



99 
96 
84 
77 
69 
60 
50 
30 



99 
96 
84 
77 
69 
60 
50 


% 




30 


m 








The absorption of the aggregate was determined as follows : 
The sand was dried to constant weight and cooled to room tempera- 
ture in a desiccator. A 500-g. sample was placed in a 500-cc. volumetric 
flask and the 1 volume of water necessary to fill to mark carefully meas- 
ured. At frequent intervals the flask was filled to mark. The zero 
volume was obtained in the same manner, except that the sand was coated 
with kerosene to prevent absorption of water. This is an adaptation of 
Rea's method for determining specific gravity of fine aggregates.* 

The coarse aggregate was dried to constant weight, cooled to room 
temperature and weighed, then immersed in water at room temperature. 
At frequent intervals it was removed from the water, quickly surface- 
dried with a towel and weighed. Our experience with these methods 
indicates that the absorption at about 3 hours gives the best results in 
estimating the quantity of water necessary for concrete mixes. 



•See "Apparent Specific Gravity of Non-Homogeneous Fine Aggregates," 
by A. S. Rea, Proc. A. S. T. M., Part II, 1917. 



4 Structural Materials Research Laboratory 

Proportioning and Mixing Concrete. 

In all the tests included in this report the concrete consisted of a 
1-4 mix by volume; that is, 1 volume of cement to 4 volumes of mixed 
aggregate, considering 94 pounds of cement as 1 cubic foot. This mix 
is equivalent to the l-V/2-3 or 1-2-3 mixes generally used for one-course 
concrete road construction. The exact equivalent of our 1-4 mix when 
expressed in the customary manner will depend on the size and grading 
of the aggregate. 

The concrete was mixed by hand in the manner regularly followed 
in making such tests in this laboratory. Each specimen was made from 
a separate batch of about % cubic foot, which was proportioned separately 
and mixed with a bricklayer's trowel in a shallow metal pan. This method 
leaves no uncertainty as to the exact quantities of materials in each 
specimen. 

Table 3 — Miscellaneous Tests of Aggregates. 



Test 


Sand 


Pebbles 


Crushed 
Lime- 
stone 


Sand 

and 

Pebbles 


Sand 

and 

Limestone 


Unit Weight of Dry Aggregate 
lb. per cu. ft. 

Absorption of Aggregate t 


115.5 

2.3 
1.3 


112.5 

2.2 
1.3 

2.3 

8.8 


99.5 

1.6 
1.0 

5.2 

12.3 


131.0 


123.0 








Abrasion Test t 
Loss in weight — per cent. 






Rea's method 









tAfter immersion in water at room temperature for 3 hrs. 

JAbrasion tests were made in the Deval abrasion testing machine. In the Standard 
method a sample of 50 pieces weighing 5000 g. was placed in the test chamber and run for 10,000 
revolutions. Rea's method was first used by A. S. Rea, of the Ohio State Highway Department, 
Columbus. It consists in using a 5000-g. sample, made up of 2500 g. of aggregate H to % in. in size 
and 2500 g. of aggregate % to 1% in- In addition to the aggregate six V/& in. cast-iron balls were 
placed in the test chamber as an abrasive charge. The entir e sample was run for 10,000 revolutions. 
It will be seen that Rea's method is much more severe than the Standard method. 



The term "consistency" as used in this report refers to the plasticity 
of the concrete; that is, the relative and not the actual quantity of mixing 
water. It has been found convenient to express the quantity of water 
used in the concrete in terms of the volume of cement. This so-called 
water-ratio has been shown to be the best criterion of the strength of 
the concrete. 

The consistency which we have called "normal" (relative consistency 
= 1.00) is of such a plasticity that a 6 x 12-inch cylinder of 1-4 concrete 
will "slump" l / 2 to 1 inch upon removal of the metal form by a steady, 
upward pull immediately after molding the specimen. Concrete of relative 
consistency of 1.10 will show a slump of 5 to 6 inches; 1.25, a slump of 
8 to 9 inches. 



Wear and Strength of Concrete 5 

Test Pieces. 

This report covers compression tests of 6 x 12-inch concrete cylinders 
and wear tests on concrete blocks 8 inches square and 5 inches in thickness. 

The 6 x 12-inch cylinders were molded in metal forms made of 12-inch 
lengths of 6-inch inside diameter cold drawn steel tubing, which had been 
split along one element by means of a thin slotter. The form was closed 
by a circumferential band. Each form stood on a machined, cast-iron 
base plate. A thin sheet of paraffined tissue paper was placed between 
the base plate and the cylinder form. 

In molding the cylinder the form was filled about one-third full and 
the concrete puddled with a ^-inch steel bar about 21 inches long. Filling 
and puddling were continued until the form was full. The top was 
leveled off with a bricklayer's trowel. About 3 to 4 hours after molding, 
a thin layer of neat cement paste (which was mixed at the same 
time or before the concrete) was spread over the top of the cylinder. 
A piece of plate glass and a sheet of paraffined paper were used to 
form a cap, which made a smooth, square end for loading. The glass 
remained in place until the form was removed. This method of capping 
is much better than setting the specimens in plaster of paris or a cement- 
plaster mixture immediately before testing. It has the following ad- 
vantages : 

(1) The cap is just as strong and stiff as the concrete and forms 
an integral part of the specimen. 

(2) The time and labor required is a small part of that necessary 
with the plaster method. 

(3) The plate glass prevents evaporation of water during the period 
the concrete is in the form. 

(4) The cylinder is ready for test at any time without further prep- 
aration. 

The metal forms for the wear blocks were made in gangs of three. 
The form was set on a sheet of building paper laid directly on the con- 
crete floor. The form was filled before puddling. The top was leveled 
off with a trowel. After a period of one to two hours the tops of the 
blocks were finished by hand with a wood float. Instead of capping, the 
blocks were covered with a sheet of wet building paper and about 3 
inches of damp sand. This method prevented loss of water while the 
blocks were in the forms. 

All test pieces were allowed to remain in the metal forms over night. 
Upon removal of the forms they were stored in the manner indicated 
in Table 4. Two cylinders and five wear blocks were made in each group 
before the duplicate sets were begun. The duplicate sets were made 
two to four weeks after the first. 

Methods of Testing. 

The compression tests of concrete were made in a 200,000-pound Olscn 
universal testing machine. A spherical bearing block was used on top 
of the cylinders. 



6 Structural Materials Research Laboratory 

Wear tests of concrete were made in the Talbot-Jones rattler. The 
test pieces consist of blocks 8 inches square and 5 inches in thickness. 
The blocks are arranged around the perimeter of the drum of the rattler, 
as shown in Fig. 1. Ten blocks constitute a test set. The ten-side polygon 
formed by the test blocks presents at nearly continuous surface. The 
outside diameter of the polygon thus formed is 36 inches and the inside 
diameter 26 inches. During the test the front of the chamber is closed 
by means of a light steel plate. The abrasive charge consists of 200 
pounds of cast-iron balls (about 133 1% inches and 10 3^4 inches in 
diameter). These balls conform to the requirements for the standard 
rattler test of paving brick of the American Society for Testing Ma- 
terials. 




Fig. 1 — Talbot-Jones Rattler with Concrete Wear Blocks in Place. 
Wear tests were made on blocks 8 inches square, 5 inches 
thick. 

The test consists of exposing the inner faces of the concrete blocks 
to the wearing action of the charge for 1800 revolutions at the rate of 
30 revolutions per minute. The machine was run for 900 revolutions in 



Wear and Strength of Concrete 7 

one direction, then reversed. Two sets of blocks are tested at once in 
the machine now in use. Each block was weighed upon removal from 
the form, upon removal from the damp sand, immediately before and 
after testing. The loss in weight during the test is used as a measure 
of the wear. This loss is reduced to an equivalent depth of wear in 
inches. 

Absorption tests were made on two wear blocks from each set of 10. 
The tests were made when the blocks were about one year old, after hav- 




Fig. 2 — Talbot- Jones Rattler with Head Closed Ready for Test. 

The machine was operated for 1800 revolutions at 30 revolu- 
tions per minute. The abrasive charge consisted of 200 pounds 
of cast-iron balls. 



ing been stored in the open air in the laboratory during the period fol- 
lowing the wear test. The blocks were dried to approximately constant 
weight on a steam radiator, weighed and immersed in water at room 
temperature. At various intervals they were removed from the water, 
allowed to drain for about 5 minutes and weighed. The gain in weight 
was reduced to an equivalent volume of absorbed water. 



Structural Materials Research Laboratory 



Discussion of Tests. 

The tests included in this report consisted of compression tests of 
120 6 x 12-inch concrete cylinders and 300 wear tests of 8 x 8 x 5-inch 
blocks, as well as miscellaneous tests of cement and aggregate. A 1-4 
mix was used throughout, with aggregate graded up to 1J4 inches. In 
general the coarse aggregate was pebbles ; in one group of tests a crushed 
limestone was used. This mix is approximately the same as that gen- 
erally used in one-course concrete road construction. Four different 
curing conditions were used for pebble aggregate as follows : 

(1) Damp sand 4 months, tested damp. 

(2) Damp sand 21 days, air 99 days. 

(3) Damp sand 3 days, air 117 days. 

(4) Air of laboratory for entire curing -period of 4 months. 
Group (1) was repeated, using crushed limestone as coarse aggregate. 

All compression and wear tests were made at age of 4 months. Average 
values from the strength and wear tests are given in Table 4. 
eooo 




> /.00 /./O /.PO tX) /tfo /so 

/rk/of/V<? Ccy?^/s/er?cy of ' Cbsrc/vfe 

Fig. 3 — Effect of Quantity of Mixing Water on the Strength of 
Concrete. 

Compression tests of 6 x 12-inch cylinders at age of 4 months. 
Each value is the average of four tests made on two different 
days. Same data as in Fig. 5. 

Effect of Quantity of Mixing Water on the Strength of Concrete. 

Fig. 3 gives the results of the tests on the effect of quantity of mixing 
water on the compressive strength of concrete. A separate curve has 
been drawn for each curing condition. An average curve from these 
tests will be found in Fig. 8. The remarkable influence of the quantity 
of mixing water on the strength, other factors being the same, is clearly 
shown by these curves. It will be remembered that the consistency which 
we have called 1.00 (normal consistency) is such that a 1-4 mix gives a 



Table 4 — Wear and Compression Tests of Concrete. 

Hand-mixed concrete. Mixed 1-4 by volume. Age at test, 4 months. 
Aggregate graded 0-l}4 in- 

The same sand used in all tests. 

Coarse aggregate consisted of pebbles or crushed limestone of the same grading. 
' The specimens were stored for the period shown in damp sand, the remainder of the time 
in the air of the Laboratory. 

Wear tests made in Talbot-Jones rattler— total of 1S00 revolutions. 

Wear tests are average of five 8 by 8 by 5 in. blocks. 

Compression tests are average of two 6 by 12-in. cylinders. 

The second set of tests in each group was made 2 to 4 weeks after the first. 





Mixing 
Water 


Depth of Wear — Inches 
8 by 8 by 5-Inch Blocks 


Compressive Strength 

—Lbs. Per Sq. In. 
6 by 12-Inch Cylinders 


Coarse Aggregate 


>> 

• — m 
*"§ 

SO 


« 

1 


-3 
c 

CO 

<s q 


T3 
C C 

— d 
tnCO 

p s 


T3 


c a 
•-co 
s? « 

*2 
Q ^ 


0) 
bO 
CJ 
U 

o 
02 
u 

< 


-a 
a 
a 
CO „ 

e w 

r - 


T3 

c c 

S 

03 CO 


T3 

c = 

•"co 

OS C 
I 


© 

M 

d 
u 

O 

CO 
h 

< 


Pebbles 


.90 
.90 


.66 
.66 


.53 
.54 

.54 

.48 
.52 

.50 


.34 
.51 

.43 


.82 
.84 

.83 


1.29 
.91 

1.10 


4970 
4990 

4980 

5970 
5700 

5890 


5310 
5150 

5230 


2890 
2720 

2810 


2110 


Crushed Limestone 


2260 
2190 






























Pebbles 


1.00 
1.00 


.73 
.73 


.54 
.52 

.53 

.34 
.46 

.40 


.52 
.41 

.47 


.83 
.78 

.81 


1.01 
1.10 

1.06 


5530 
4760 

5200 

5800 
5280 

5540 


4550 
4960 

4760 


3040 
2960 

3000 


2290 




2020 
2160 






























Pebbles 


1.10 
1.10 


.81 
.81 


.52 
.56 

.54 

.48 
.52 

.50 


.51 

.54 

.53 


1.00 
.98 

.99 


1.23 
1.02 

1.12 


4470 
5020 

4750 

5390 
5540 

5470 


3940 
4220 

4080 


2350 
2410 

2380 


2240 


Crushed Limestone 


2050 
2150 






























Pebbles 


1.25 
1.25 


.91 
.91 


.57 
.63 

.60 

.58 
.56 

.57 


.51 
.56 

.54 


.96 
1.25 

1.10 


1.56 
1.64 

1.60 


4700 
4490 

4600 

4320 
4850 

4590 


4350 
3640 

4000 


2360 
1900 

2130 


1640 


Crushed Limestone 


1710 
1680 






























Pebbles 


1.35 
1.35 


.99 
.99 


.59 
.66 

.63 

.59 
.61 

.60 


.69 
.69 

.69 


1.49 
1.61 

1.55 


2.40 

1.51* 

1.51 

1.51* 


3860 
3650 

3760 

3910 
3820 

3870 


2570 
3190 

2880 


1400 
1310 

1360 


1420 


Crushed Limestone 


1250 
1340 






























Pebbles 


1.50 
1.50 


1.09 
1 09 


.74 

.73 

.73 

.60 

.68 

.64 


.85 
.92 

.89 


2.34 
2.00* 

2.00* 


1.68 
1.68 


3740 
3530 

3640 

2640 
3190 

2920 


2300 
2440 

2370 


1330 
1090 

1210 


1280 


Crushed Limestone 


1240 
1260 































•Omitting one badly damaged block. 

fOne block disintegrated, allowing entire charge to fall out after about 1100 revolutions. 



10 



Structural Materials Research Laboratory 



slump of J^ to 1 inch when the form is slipped off the' freshly molded 
cylinder. A consistency of .90 contains 90 per cent, of the amount of 
water required for normal consistency; a consistency of 1.5.0 contains 
\ l / 2 times the quantity of water used in the normal consistency concrete, 
etc. The normal consistency concrete may be characterized as plastic; 
the .90 is somewhat dry; the 1.50 quite wet, but contains much less water 
than the "sloppy" mixes frequently seen in reinforced concrete work. 
It will be noted that there is a rapid falling-off in strength as the 
water content is increased from normal consistency. With a consistency 




.SO /.OO /.SO 2.00 2SO 3.00 3.SO 

Wafer- Path to Ifo/ume of Cement j¥ m x 

Fig. 4 — Effect of Quantity of Mixing Water on the Strength of 
Concrete. 

Compression tests of 6 x 12-inch cylinders at age of 28 days. 
Each value is the average from five tests. Details of tests not 
given in this report. 

of 1.25 the strength is reduced to about 75 per cent, of the' highest; with 
a consistency of 1.50 the strength is only one-half that which may be 
obtained with the same cement content. For wetter mixes the strength 
would be still further reduced. 

In general it will not be feasible tp use concrete of a consistency 
which will give maximum strength, since it is somewhat too stiff for satis- 
factory workability. In concrete road work where hand finishing is used 
the concrete must be mixed to a consistency varying from 1.10 to 1.15. 
In other words, we must sacrifice a portion of the possible strength of 
the concrete in order to secure a workable mix. This consistency will 
give a slump of 5 to 7 inches. If machine finishing is employed the con- 
crete can be mixed to a consistency corresponding closely to maximum 
strength. In reinforced concrete work there is in general little excuse 
for using mixes wetter than 1.25 consistency, corresponding to a slump 
of 8 to 9 inches. 



Wear and Strength of Concrete 11 

The average curves in Fig. 8 have been platted in terms of the water- 
ratio instead of the relative consistencies, although relative consistencies 
are also shown. The water-ratio is the ratio by volume of water to cement 
in the batch. 

Further Discussion of Effect of Quantity of Mixing Water on the 
Strength of Concrete. 

Many series of tests made in this laboratory have fully established 
the fundamental importance of the quantity of mixing water on the 
strength of concrete. 

Fig. 4 gives the average values from a series of tests of this kind 
in which the compressive strength is platted against the water-ratio of 
the concrete. In this series the mixes ranged from 1-15 up to neat cement. 
The consistencies were varied over a wide range. The size of the aggre- 
gate ranged from a very fine sand to a coarse concrete aggregate, for all 
combinations of mix and consistency. Further details of these tests are 
not given in this report. 

In the figure distinguishing marks were used for each mix, but no 
distinction was made between aggregates of different sizes or concretes 
of different consistencies. When the compressive strength is platted 
against the water content in this way a smooth curve is obtained due to 
the overlapping of the points for different mixes, consistencies, etc. Val- 
ues from the dry concretes have been omitted from the diagram; if these 
were used we should obtain a series of curves dropping downward to 
the left from the curve shown. It is seen at once that the size and grading 
of the aggregate and the quantity of cement are no longer of any import- 
ance except in so far as these factors influence the quantity of mixing 
water required to produce a workable concrete. This gives an entirely 
new conception of the function of the constituent materials entering into 
a concrete mixture. 

The equation of the curve in Fig. 4 is of the form 

A 

S= 

B* 
where 5" is the compressive strength of the concrete and x is the ratio 
of the volume of water to volume of cement in the batch (water-ratio). 
A and B are constants whose values depend on the quality of the cement 
used and on other conditions of the test. 

The values of the constants in these tests are shown on the diagram. 
This equation expresses the law of the strength of concrete so far as 
variations in the proportions of materials are concerned. It is seen that 
for given concrete materials the strength depends on only one factor — 
the water-ratio. Equations which have been proposed for this purpose 
in the past contain terms which take into account such factors as quan- 
tity of cement, proportions of fine and coarse aggregate, voids in aggre- 
gate, etc., but they have uniformly omitted the only item which is of 



12 Structural Materials Research Laboratory 

any importance; that is, the water. The relation given above holds so 
long as the concrete is not too dry for maximum strength, and the aggre- 
gate not too coarse for a given quantity of cement; *in other words, sc 
long as we have a workable concrete. 

The strength of the concrete responds to changes in water, regard- 
less of the reason for these changes. The water-ratio may be changed 
due to any of the following causes: 

(1) Change in mix (cement content). 

(2) Change in size or grading of aggregate. 

(3) Change in relative consistency. 

(4) Any combination of (1) to (3). 

In certain instances a 1-9 mix is as strong as a 1-2 mix, depending 
only on water content. It should not be concluded that these tests indi- 
cate that lean mixes can be substituted for richer ones without limit. 
We are always limited by the necessity of using sufficient water to secure 
a workable mix. So in the case of the grading of aggregates. The work- 
ability of the mix will in all cases dictate the minimum quantity of water 
that can be used. The importance of the workability factor in concrete 
is therefore brought out in its true relation. 

The problem of designing concrete mixes resolves itself into this: 

To produce a workable concrete with a given water-ratio using a 
minimum of cement; or the converse, to produce a workable concrete 
which has the lowest water-ratio for a given quantity of cement. The 
methods of securing the best grading of aggregate and the use of the 
driest practicable concrete are seen to be only devices for accomplishing 
the above-mentioned results. A forthcoming Bulletin on the "Design of 
Concrete Mixtures"* will give further details of the principles underlying 
the proportioning of concrete, arid discuss their application to practical 
problems. 

The influence of the water-ratio of concrete on its strength will be 
shown by the following considerations : One pint more water than neces- 
sary to produce a plastic concrete in a 1-4 mix reduces the strength to 
the same extent as if we should omit 2 to 3 pounds of cement from a 
one-bag batch. 

Our studies give us an entirely new conception of the function per- 
formed by the various constituent materials. The use of a coarse, well- 
graded aggregate results in no gain in strength unless we take advantage 
of the fact that the amount of water necessary to produce a plastic mix 
can thus be reduced. In a similar way we may say that the use of more 
cement in a batch does not produce any beneficial effect, except from the 
fact that a plastic, workable mix can be produced with relatively less 
water. ' 

The reason a rich mixture gives a higher strength than a lean one 
is not that more cement is used, but because the concrete can be mixed 
(and usually is mixed) with a lower water-ratio in the case of the richer 
mixtures than for the lean ones. If advantage is not taken of the fact 



c See Bulletin 1, Structural Materials Research Laboratory. 



Weab and Strength of Concrete 



13 





























k 


- — 






j . J ■ 




S- 










•^/■oo 






-4 


1 


f 


^ 


^ 






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/ 


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V 












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!/ 


/ / 






^>£>6/e> ^?<?/-<ftp>c/e- 






w 


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Fig. 5- 



^ sooo 



^ /OOO 



f& 40 60 SO /OO /fO 

CosrcyTsfe S/bnac//sh> ZP^^zo ib/7c/-^_/j 

-Effect of Curing Conditions on the Compressive Strength of 
Concrete. 

Compression tests of 6 x 12-inch cylinders at age of 4 months. 
Each value is the average of four tests made on two different 
days. Same data as in Fig. 3. 

?/? 




/oo //o ^o /JO /40 /JO 

Fig. 6 — Effect of Quantity of Mixing Water on the Wear of Con- 
crete. 

Wear tests of 8 x 8 x 5-inch blocks at age of 4 months. Each 
value is the average of 10 blocks made on two different days. 
Same data as in Fig. 7. 

that in a rich mix relatively less water can be used, no benefit will be 
gained as compared with a leaner mix. In all this discussion the quan- 
tity of water is compared with the quantity of cement in the batch (cubic 
feet of water to one sack of cement) and not to the weight of dry ma- 
terials or of the concrete, as is generally done. 



14 



Structural Materials Research Laboratory 



For the other curves showing the strength water-ratio relation, see 
paper on "Time of Mixing Concrete," referred to above. 

Effect of Quantity of Mixing Water on the Wear of Concrete. 

Figs. 6 and 8 give the results of tests to determine the effect of 
quantity of mixing water on the wear of concrete. It will be noted that 
the depth of wear is expressed in inches. The wear-water-ratio relation 
is just opposite to that found in the strength tests; in other words, a 
high strength is accompanied by low wear, and vice versa. If the wear 



P.OfO- 

/& 
\ /-p 

< .8 



\ 
























\ 
























\ 






a) 


>r /- 


4 fy\ 










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/C&Zt&'e- sl<?c?/-£><?a/£ 










1) 


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1 








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v\ 


^ 


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\2. 


\Sf&>™ e ' 


s<? CyS/5/grZ£X- 


























b^r 


















<-Jo 


o 


.fo 









































O PO <?0 60 SO /OO /fO 



Fig. 7 — Effect of Curing Conditions on the Wear of Concrete. 

Wear tests of 8x 8 x 5-inch blocks at age of 4 months. Each 
value is the average of 10 blocks made on two different days. 
Same data as in Fig. 6. 



curve in Fig. 8 were inverted we should have almost a duplicate of the 
strength curve. In general, the lowest wear is found at about the same 
water-ratio as the highest strength. The average curves (Fig. 8) show 
that maximum strength and minimum wear come at a consistency of 
about .95, or a water-ratio of about .70. It should be pointed out that for 
other mixes the best results would probably be found at about the same 
relative consistency, but at a different water-ratio. For a given con- 
sistency the water-ratio is higher for lean mixes and lower for rich 
mixes. 

The relation between the' depth of wear and the water-ratio of the 
concrete for blocks stored for 21 days in damp sand is expressed by the 
equation 

, W = 0.15 (4.8 X ). 

Where W is the depth of wear expressed in inches, and x (an expo- 
nent) is the water-ratio. A similar relation was found in the series of 
wear tests in the paper on "Time of Mixing Concrete," referred to above. 



Wear and Strength of Concrete 



IS 



500O 





















,/! 






-^ 










y 












f^ 


,1 




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T 




"V- *T^I 




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♦ 








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/1//X /-tf 6j 


/ V&i/srr? 








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J& 



.£0 70 .ffO 90 400 4/0 



ON 



the Strength and 



Fig. 8 — Effect of Quantity of Mixing Water 
Wear of Concrete. 

Average curves from Figs. 3 and 6. The quantity of mixing 
water is expressed as a ratio to the volume of cement in the 
batch. Each value for compression is the average of 20 tests 
(four curing conditions). Each value for wear is the average 
of 50 tests (four curing conditions). In interpreting this diagram 
it should be borne in mind that we have averaged the four storage 
conditions described in Table 4. For best curing conditions the 
concrete will show a higher strength and much less wear than 
any indicated by these curves. 

Water Required for Concrete Mixes. 

Since the quantity of mixing water exerts such an important influence 
on the strength and other properties of concrete, it will be of interest 
to examine the factors which influence the amount of water required for 
satisfactory results. The function of water in concrete is twofold: 

(1) To supply the water necessary for hydration of the cement. 

(2) To produce a plastic mixture. 

Without regard to the actual quantity of mixing water, the following 
rule is a safe one to follow: 

"Use the smallest quantity of mixing water that will 
produce a workable mix." 

The importance of methods of proportioning, mixing, handling, plac- 
ing or finishing concrete which will enable the builder to reduce the water 
content to a minimum is at once apparent. 

While the exact quantity of water required under (1) has not been 
determined except in certain instances, it is generally agreed that the 
quantity used in concrete is greatly in excess of that necessary for hydra- 



16 



Structural Materials Research Laboratory 



tion of the cement. The bulk of the water in concrete is used in order 
to produce a plastic or workable mix. The exact quantity required for 
this purpose depends on the materials used, nature of the work, and 
methods of handling and finishing. 

It is, in general, impracticable to state in definite quantities the 
amount of water which should be used, since this depends on many dif- 
ferent factors, such as the following: 

(1) The relative consistency which must be used, which is dictated 
by the nature of the work. 

(2) The> normal consistency of the cement. 

(3) The quantity of cement. 

(4) The size and grading of the aggregate. 

(5) The absorption of the aggregate. 

(6) The moisture content of the aggregate. 

(7) Admixtures which may be used. 

A water formula has been developed which takes into account all 
these elements ; for further details see Bulletin 1 of the Structural Ma- 
terials Research Laboratory, "Design of Concrete Mixtures." 

The quantity of water which affects the water-ratio as given in Fig. 8 
is only such a part of the whole as affects the cement. In other words, 
the water which is absorbed by the aggregate is not considered as in- 
fluencing the water-ratio. This makes it plain that the absorption of the 
aggregate must be taken into account if concretes from widely different 
aggregates are being compared. Many serious errors have been made 
in drawing conclusions from tests, due to failure to take into account 
the influence of absorption, grading of aggregates, etc., on the water 
content of the concrete. 

In general, it is impracticable to determine in advance the exact 
quantity of water required for concrete mixes, largely due to two causes : 
(1) Inability to determine in advance the lowest relative consistency 
which may be used and still produce a workable concrete; (2) varying 
moisture content of aggregates. 

The following table may be of interest in indicating the approximate 
quantities of water necessary for certain mixes. It is assumed that a 
well-graded aggregate up to V/i inches in size will be used. Only under 
the most favorable conditions can the minimum values be used; in gen- 
eral, the maximum values need not be exceeded. 



Mix 


Approximate Mix as Usually- 
Expressed 


Water Required 

(Gallons per Sack 

of Cement) 


Cement 


Volume of 

Aggregate 

After Mixing 


Cement 


Aggregate 


Minimum 


Maximum 




Fine 


Coarse 




1 

1 
1 
1 


5 

4 
3 


1 
1 
1 


2 

2 


4 
3 
3 

2V 2 


6 

5V 2 
5 


6H 

6 
5K 



Wear and Strength of Concrete 



17 



Effect of Curing Condition on the Strength of Concrete. 

The effect of curing condition on the compressive strength of con- 
crete is shown in Fig. 5 ; an average curve is given in Fig. 9. All con- 
sistencies of concrete show great increases in- strength under favorable 
curing conditions as compared with specimens which were allowed to 
dry out at once. The dryer mixes show a more rapid improvement due 
to storage in a damp place during the first few days than the wetter 
ones. Even 3 days in damp sand shows an increase in strength of the 
dryer concretes of about 35 per cent, as compared with the specimens 
stored in open air for the entire period. It should be borne in mind that 









sooo 



























1 
























\ 
























\ 

\ 
























\ 


/ 


•f 






















( 
























\ 






















1 




5k„ % 






tv& 


2f_ 










. 4) 


































*/-< 


t£>y 


I'd,, 


/.^?e 



























































/.so 



/es 



Fig. 9- 



.Jk? 



~ O <K> fO SO SO 

Cosrc/T-fe Jtbrw/fo P&srj/O S&s?e/- c/cy^ 

-Effect of Curing Condition on the Strength and Wear of 
Concrete. 

Average curves from Figs. 5 and 7. Each value for com- 
pression is the average of 24 tests (four each for six consisten- 
cies). Each value for wear is the average of 60 blocks (10 each 
for six consistencies). The upward trend of the wear curve 
results from the abnormal wear of the 4-month sand-stored 
blocks on account of being tested in damp condition. 



in the most unfavorable case used in the experiments the concrete was in 
the steel form for 1 day with only the top exposed, consequently the 
conditions were more favorable than those frequently found in summer 
weather or in arid regions where the concrete is exposed to rapid evapora- 
tion of the mixing water from the moment it is placed. 

The concrete stored for 4 months in damp sand and tested damp 
is 2J/2 to 3 times as strong as similar concrete which has been exposed 
to room atmosphere for the same period. Protecting the concrete from 
drying out for only 10 days (taking values from Figs. 5 and 9) gives an 
increase in strength of about 75 per cent, for the dryer mixes. 



18 Structural Materials Research Laboratory 

Effect of Curing Condition on the Wear of Concrete. 

The effect of curing condition on the wear of concrete is no less 
striking than the effect on the strength. 

It will be seen in Fig. 7 that the blocks stored for the entire period 
of 4 months in damp sand showed more wear in most instances than those 
which had been stored for 21 days in damp sand and the remainder of 
the time in air. This peculiar result is no doubt due to the fact that the 
concrete was tested in a damp condition, and does not indicate that the 
longer period in damp sand is injurious. The comparison would have 
been more nearly correct if the blocks had been allowed to dry out a 
few days before testing. These results do show that concrete in a wet 
or damp condition suffers more from wear than when dry. It is a 
matter of common experience that non-metallic materials, such as timber, 
terra cotta, concrete, stone, etc., which absorb water, show a lower strength 
in a wet condition than when dry. Additional tests will be required to 
show the exact effect of moisture content on strength and wear of con- 
crete, other factors being the same. 

It is not necessary to speculate on the probable effect of moisture in 
the concrete in order to secure valuable information from these tests. 
The dryer mixes show an increase in wear from .50 inch for concrete 
stored in damp sand for 21 days, to 1.10 inches for concrete in air for 
entire period; the tests indicate that 10 days in damp storage would give 
a wear of about .65 inch. For the wetter mixes the wear after 21 days 
in damp sand is about .85 inch; for 10 days 1.15 inches; for air storage 
throughout probably 2 inches. In the wetter consistencies the tests were 
not carried to completion on account of disintegration of certain blocks, 
which caused the entire ring to collapse. 

The photographs in Figs. 16 to 21 show side views of the blocks 
after test. The effect of both consistency and curing condition are clearly 
shown by the relative thickness of the blocks. 

Recapitulation of Effect of Consistency and Curing Condition. 

In view of the important influence of consistency and curing condi- 
tions of concrete shown by these tests, it seems doubtful if there is any 
phase of concrete work which will pay such high dividends as a little 
care to see that proper consistency is used and desirable curing conditions 
are provided. In many instances the quality of the concrete could be 
vastly improved at trifling expense, but nothing is done because those in 
charge do not appreciate the importance of care in these directions. The 
writer is convinced that practically all of the faults from concrete floors 
follow from these two causes. Excessive wear and dusting are certain 
to result in a floor in which the concrete is never allowed to have the 
water necessary for hydration of the cement. It is notable that dusting 
never occurs on a concrete road, for the reason that it gradually gets the 
water necessary for hydration from rain or snow. However, due to low 



Wear and Strength of Concrete 



19 



wearing resistance at early periods, resulting from premature drying, it 
may be badly worn before rain comes. 

An excess of mixing water is a serious fault in concrete. If, in addi- 
tion to too much water the concrete is allowed to dry out at once it is 
almost certain to be a failure if subjected to wear and will give very 
low strength. For the two wettest consistencies and the two most un- 
favorable curing conditions, the compressive strength of the pebble con- 
crete was 1300 pounds per square inch ; for the two most favorable curing 
conditions and the three dryest consistencies the average compressive 







.6 .a to /? i* *6 
k/eor — /nches 

Fig. 10 — Relation between the Compressive Strength and Wear of 
Concrete. 

Compression tests of 6 x 12-inch cylinders, and wear tests of 
8 x 8 x 5-inch blocks at age of 4 months. Each value is based on 
the averages of four compression tests and 10 wear tests. All 
consistencies and curing conditions are included. 

strength was 4850 pounds per square inch — an increase of 275 per cent. 
In the case of the wear tests the corresponding values are 1.70 inches and 
.50 inch; an increase of 240 per cent. The comparison in the wear test 
is not as unfavorable as it should have been, since the poorer blocks 
broke up before the test was completed. 

Proper curing of concrete is second only in importance to the control 
of water content. The rule stated above with reference to water content 
may now be extended to the following: 

Use the smallest quantity of mixing water that will 
produce a workable concrete, then allow the concrete to 
have as much water as possible during the period of 
curing. 



20 



Structural Materials Research Laboratory 



All concrete should be protected against premature drying for at 
least one week, and longer if practicable. This period should be extended 
to 10 days or two weeks in cool weather, or where the concrete is to be 
subjected to heavy traffic at an early age. 

Covering with damp sand or earth, or wet burlap are excellent meth- 
ods of curing. The practice of "ponding" is common in road construction. 
The writer wishes to offer a word of caution with reference to the use 
of wet sawdust for covering concrete floors. Sawdust may have most 
harmful results, on account of the organic acids present. 



eooo 
ssoo 



\ 4SOO 

*3 



£ jsoo 



<0 

































































Af/A 


t-4 






















figeot test 


tma 




















































































si 


&> 


























* 












































• 7S 





























4 .s .6 .7 .<y s to /.z /& ic te to 

h/eor- fne/ies \/of- Sca/e) = JV 

Fig. 11 — Relation Between Compressive Strength and Wear of Con- 
crete. 

Same data as in Fig. 10, except curve plated on logarithmic 
scales. The points shown are taken from the curve in Fig. 10. 

Compression tests of concrete made in other series show that the 
strength of concrete increases indefinitely, so long as it is not permitted 
to dry out* 



Relation Between Strength and Wear of Concrete. 

The relation between strength and wear of concrete in this series is 
shown in Fig. 10. All tests have been platted. Each value is based on the 
average of four compression tests and 10 wear tests. This diagram 
shows that a definite relation exists between strength and wear at least for 
the conditions of these tests ; that is, for concrete of different consistencies 

•See "Effect of Age on the Strength of Concrete," by D. A. Abrams, 
Proc. American Society for Testing Materials, Part II, 1918. 



Wear and Strength of Concrete 



21 



and curing conditions. Further tests will be necessary to show whether 
or not this relation is entirely general for other aggregates, etc. 

Fig. 11 is the same curve platted to log. scale. The straight line in 
this diagram enables us to devise the equation: 

2230 



S = 



W 1 - 07 
as showing the relation between the variables ; where S = compressive 
strength in pounds per square inch and W = the depth of wear in inches. 
A similar relation from another series of strength and wear tests 
made in this laboratory will be found in Figs. 14 and 15 of the paper on 
"Effect of Time of Mixing," referred to above. 






\* 



i 



%> 

** 
U 























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rf& 
















r& 


i 












0$ 




f£ 


&te?y/ 














lZ 




< T4>$r 




















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- 


y!s 






























































A//* / 


-*6y 14 


z>sL-s-, 


«*£» 









































































































.*? 



<ec& VO /J& 4JO 440 45& 

Fig. 12 — Effect of Quantity of Mixing Water on the Absorption of 
Concrete. 

Absorption tests of 8 x 8 x 5-inch blocks. Pebble aggregate. 
Age 1 year. Absorption determined after immersion in water at 
room temperature. Each value is the average of eight blocks 
from four different curing conditions — one block from each set 
of pebble aggregates in Table 5. Absorption is given by volumes ; 
absorption by weight is about 40 per cent, of these values. 

In the earlier series of tests the relation between strength and wear 
of concrete was expressed by 

1800 
S= 



W 1 - 30 
The agreement between the equations from the two different series 
of tests is quite close when we consider that the earlier series was tested 
at 2 mo. and the latter at 4 mo. 



22 Structural Materials Research Laboratory 

Comparison of Pebble and Crushed Stone Aggregate. 

Crushed limestone was used as coarse aggregate in one group of 
tests. In general the limestone concrete gave somewhat higher strength 
and lower wear than the gravel concrete using the same sand and the 
same water and cement. However, the tests do not cover a sufficient 
range to justify definite comparisons of the merits of the two types of 
aggregate. Both of the aggregates used in this series were of high grade 
and gave good results in the tests. Other tests now under way and 
planned for the future are expected to give definite information on the 
relative merits of different aggregates. 

Method of Making Wear Tests. 

The Talbot-Jones rattler has been found entirely successful as a 
method of studying the wear of concrete in the laboratory. The results 
of the tests thus far completed and the definite relations found between 
the wear and strength have given considerable confidence to this method 
of testing. The abrasive charge of 200 pounds of cast-iron balls, and the 
rate and number of revolutions used, gives a wearing action suited for 
a wide range in the properties of concrete. A very poor concrete may 
be entirely destroyed, a high-grade concrete will show a wear of l / 2 inch 
or less. 

The test gives a combination of abrasion and impact that cannot be 
withstood by an inferior concrete. The severity of the impact may be 
seen from the fact that frequently the 1^-inch cast-iron balls are broken 
during the test. While the test does not fully duplicate the action of 
traffic, it furnishes a valuable guide to the relative effects of different 
methods of treatment, materials, etc., for use in pavement construction. 

This method of making wear tests of concrete is believed to have 
the following advantages as compared with other methods which have 
been used or proposed for this purpose : 

(1) The concrete is subjected to a treatment which ap- 
proximates that of service. 

(2) The test piece is of usual form and of sufficient size 
that representative concrete can be obtained. 

(3) The test pieces are convenient to make, store and handle, 
and require a relatively small quantity of concrete. 

(4) The cost of tests is not excessive. 

(5) The machine used is found in a number of testing 
laboratories. 

(6) The wearing action takes place on the top or finished 
surface of the concrete. This makes it possible to study the 
effect of various surface treatments and finishes. 

(7) Several tests may be made at the same time, thus en- 
abling more representative results to be obtained. 



Wear and Strength of Concrete 



23 



I 

§ 9 

X* 










































































X 

^>0 


^o 


^£Z 
















\V 






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O PO 40 60 effO /OO /PO 

Fig. 13— Effect of Curing Conditions on the Absorption of Concrete. 
Absorption tests of 8 x 8 x 5-inch blocks. Absorption de- 
termined after immersion in water at room temperature. Each 
value is the average of 12 blocks from six different consistencies. 
Same data as in Fig. 12. Absorption is given by volumes ; 
absorption by weight is about 40 per cent, of these values. 



j 































A 


<f 


























/ 


: 


























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"O /OO POO JOO 400 SCO GOO 700 

Zsr?e> of"Z/77/^<?/rsy0s7-^c><z/ss 

Fig. 14 — Effect of Time of Immersion on the Absorption of Concrete. 
Absorption tests of 8 x8x 5-inch blocks. Absorption de- 
termined after immersion in water at room temperature. Each 
value is the average of 48 tests from six consistencies and four 
curing conditions. Data from Table 5. Absorption is given by 
volumes; absorption by weight is about 40 per cent, of these 
values. 



24 » 



Structural Materials Research Laboratory 



Table 5 — Absorption Tests of Concrete. 

Hand-mixed concrete. 

Mix 1-4 by volume. 

Aggregate graded 0-1 M in. 

The same sand used in all tests— torpedo sand from Elgin, 111. 

Coarse aggregate consisted of pebbles or crushed limestone of same grading. 

Age at test 1 year. The tests were made on 8 by 8 by 5-in. concrete blocks which had 
previously been used in wear tests at the age of 4 months. Immediately after molding the blocks 
were stored for the period shown in damp sand, the remainder of the time in the air in 
the Laboratory. 

During the absorption test the blocks were immersed in water at room temperature. 

Each value is the average of 2 blocks made on different days. 



Coarse 
Aggregate 



Mixing 
Water 



.3 3 

a> o 



Absorption — Per Cent, by Volume 



T3 


T3 


T3 


© 


T3 


"O 


•a 


a 


a a 


_, C 


c* 




a c 




C3 -1 


— c3 


C 03 


03 


— eS 


C e3 


GO <u 


roGQ 




o 


CO a 






ftu 


«fi 


GO 


sa 


C3fi 


c3 O 


Q c3 




03 O 


Q c3 


QoB 


SQ 


ccQ 


< 


Qto 


SQ 


ccQ 



32 



73 


T3 


■sg 


eS 


wCG 


— CO 


fr* 


>>& 


^ c3 


c3 a 


£Q 


coQ 



Pebbles 

Cr. Limestone. 

Pebbles 

Cr. Limestone. 

Pebbles 

Cr. Limestone. 

Pebbles 

Cr. Limestone. 

Pebbles 

Cr. Limestone. 

Pebbles 

Cr. Limestone. 

Pebbles 

Cr. Limestone. 

Pebbles 

Cr. Limestone . 

Pebbles 

Cr. Limestone . 

Pebbles 

Cr. Limestone. 

Pebbles 

Cr. Limestone. 

Pebbles 

Cr. Limestone. 



3 Hours 



1.00 
1.00 
1.10 
1.10 
1.25 
1.25 
1.35 
1.35 
1.50 
1.50 



.66 
.66 
.73 
.73 
.81 
.81 
.91 
.91 
.99 
.99 
1.09 
1.09 



3.17 

4.66 
4.47 
2.53 
2.58 
2.89 
5.56 
4.30 
4.58 
4.72 
4.58 
5.07 



3.93 



4.00 
'5!67 
4. '23 
(K25 



6.41 
*6*7i 

'8.18 
'§!52 

ioo 
o.'ii 



7.32 
i6!30 
l6! 20 

io!7o 
ii!e>6 



48 Hours 



.90 
.90 
1.00 
1. 00 
1.10 
1.10 
1.25 
1.25 
1.35 
1.35 
1.50 
1.50 



.73 
.73 
.81 
.81 
.91 
.91 
.99 
.99 
1.09 
1.09 



5.08 
6.74 
6.20 
4.85 
5.49 
5.26 
7.30 
6.54 
8.05 
7.91 
8.02 
8.82 



6.76 



7.06 
'9.2Q 
7'. 94 

io.ii 

i6!95 



9.06 

ib'.bb 



11.20 

iiiSo 

13 '50 



11.36 
9!89 

ii*85 
i2"66 

i2l30 
i<L45 



6 Hours 



24 Hours 



3.81 
5.15 
5.05 
3.47 

4.77 
4.16 
5.48 
5.27 
5.97 
6.23 
6.56 
5.52 



4.49 



4.50 
06 

'5.'82 
'7!63 

'i'.85 



7.70 
'7.96 

*9"!58 

"oi 
i2]8i 

ii!92 



9.53 

'8i74 
i6!66 

ii!46 
ii!6i 

i3!65 



4.99 

6.52 
6.11 
4.71 
5.11 
4.75 
5.99 
6.02 
7.21 
7.40 
7.18 
8.44 



6.26 
6i05 
8!66 
i'.QJ 



10.90 



10.60 
i6.60 
i3!60 
i3!50 



11.00 

Oi 

ii!s6 
12 .'io 
ii!90 
ii!30 



3 Days 



7 Days 



6.08 
6.03 
6.54 
5.56 
6.88 
6.20 
7.65 
7.08 
8.94 
8.35 
8.49 
9.16 



7.06 
*7i72 
*8!70 
*9!22 
10*42 
1L45 



9.35 
i6*58 
i6!74 
i3i05 
ii*75 
i3i65 



11.75 
i6!53 
i2!35 
i2!30 
i3!22 

ii!86 



6.46 
6.98 
7.24 
5.76 
6.76 
6.90 
7.42 
8.06 
8.98 
8.85 
9.92 
9.10 



7.31 
7i55 
'9i72 

9!ii 

io!2i 
io'si 



9.44 

i6!34 

ii!45 

iOo 

i4.*46 

i2!92 



11.16 
i6."90 

io!»5 
iiiso 

i2!©7 

ii!"' 



28 Days 



Pebbles 

Cr. Limestone 
Pebbles... 
Cr. Limestone 

Pebbles 

Cr. Limestone 

Pebbles 

Cr. Limestone 

Pebbles 

Cr. Limestone 

Pebbles 

Cr. Limestone 



..0 
..0 
1.00 
1.00 
1.10 
1.10 
1.25 
1.25 
1.35 
1.35 
1. 
1.50 



1.09 
1.09 



9.07 
7.54 
5.68 
5.92 
7.00 
5.64 
7.88 
8.30 
9.13 
9.43 
10.15 
9.23 



7.82 



7.84 
'<)!43 
'9!84 
i6!74 
ii!72 



9.63 
i6!92 

ii!68 

i4]25 

isios 
i5.46 



12.22 
i6!25 

ii!27 

i3J8 
16.50 



Wear and Strength of "Concrete 



25 



Table 6 — Unit Weight of Concrete. 

Hand-miied concrete. 

Mix 1-4 by volume. 

Weighed immediately before test at age of 4 months. 

Aggregate graded O-134-in. 

The same sand used in all tests. 

Coarse aggregate consisted of pebbles or crushed limestone of same grading. 
The tests were made on 8 by 8 by 5-in. blocks and 6 by 12-in. cylinders. 
Test pieces were stored for the period shown in damp sand, the remainder of the time in 
the air of the Laboratory. 

Each value is the average of 4 cylinders and 10 wear blocks. 





Mixing Water 


Weight — lb. per cu. ft. 


Coarse 
Aggregate 


Relative 
Consistency 


Water 
Ratio 


Damp Sand 
Storage 


21 Da. in 
Damp Sand 


3 Da. in 
Damp Sand 


Air 
Storage 


Pebbles 


.90 
.90 
1.00 
1.00 
1.10 
1.10 
1.25 
1.25 
1.35 
1.35 
1.59 
1.50 


.66 
.66 
.73 
.73 
.81 
.81 
.91 
.91 
.99 
.99 
1.09 
1.09 


155.8 
152.5 
157.0 
152.0 
156.9 
156.0 
155.9 
156.2 
156.9 
155.6 
154.8 
156.0 


148.5 


147.0 


147.0 






Pebbles 


153.0 


152.0 


151.0 






Pebbles 


152.0 


150.5 


149.8 






Pebbles 


152.0 


148.5 


148.0 






Pebbles 


152.0 


149.8 


150.2 






Pebbles 


149.5 


148.2 


148.0 


Crushed Limestone 














Fig. 15 — Front View of W'ear Blocks after Test. 
Top row, gravel as coarse aggregate. 
Bottom row, crushed limestone as coarse aggregate. 



26 Structural Materials Research Laboratory 

(8) Tests may be made on sections of concrete cut from 
roads which have been in service. 

(9) Other paving materials, such as brick, granite blocks, 
etc., may be tested in the same manner as the concrete. 

Absorption Tests of Concrete. 

Absorption was determined on two wear blocks from each set of 
10, after immersion in water for periods of 3 hours to 28 days. It 
should be noted that absorption tests were made on blocks at the age 
of 1 year, which had been tested for wear at 4 months. 

The results of absorption tests are given in Table 5, and in Figs. 13 
and 14. In Fig. 13 all consistencies for a given curing condition have 
been averaged. It is interesting to note that the absorption is influenced 
by the curing condition of the concrete in the same way as the wear. 
(Compare Figs. 13 and 7.) The curing condition that gives high wear, 
gives high absorption, and vice-versa. 

The effect of consistency and curing condition on absorption is 
shown by an average absorption of 5.77 per cent, for the most favorable 
conditions after 24-hour immersion and 12.6 per cent, for the most un- 
favorable conditions. The absorption is here given by volumes; the ab- 
sorption by weight would be only about 40 per cent, of these values. 

The effect of time of immersion on the absorption is shown in Fig. 
14; all consistencies and curing conditions have been averaged for a given 
time of immersion. 

Unit Weight of Concrete. 

The unit weight of all test pieces was determined immediately before 
test at the age of 4 months. The values are given in Table 6. Each 
value is the average from four cylinders and 10 wear blocks. The weight 
of the concrete is little affected by the consistency, but is greatly influenced 
by the curing condition. The weights of the specimens stored for 4 
months in damp sand cannot be compared directly with the others, since 
they contained free moisture; that is, water in the uncombined state. A 
comparison of the average weights of all consistencies for the other curing 
conditions shows that the concrete stored 3 days in damp sand took up 
.33 pound more water and that stored for 21 days in damp sand 2.16 
pounds more water per cubic foot than that stored in air throughout the 
4 months. Since all test pieces were in the same room-dry condition 
when the weights were determined, it seems that these values may be 
taken as approximate measures of the additional quantities of water 
which have entered into chemical combination with the cement, due to 
storage in a damp place for these periods. 



Wear and Strength of Concrete 



27 



BIBLIOGRAPHY 

The following list contains the more important titles to articles hav- 
ing a bearing on the subject-matter of this report. Many of the text books 
on concrete and reinforced concrete give data on the effect of consistency 
on the strength of concrete. 

Wear Tests of Concrete and Other Paving Materials 

Abrasive Resistance of Paving Materials; by J. Bauschinger. 

"Communications," Vol. 11, 1884. Drawing of machine and table 
of results in Johnson's Materials of Construction. 




Sand 4 mo 

Cft. STONE 



Fig. 16 — Side View of Blocks after Test. 
A "pavement determinator" was on exhibition in Detroit in 1912 and at 

the Chicago Cement Show, 1913. 

Concrete-Cement Age. Dec, 1912. 
An Investigation of the Concrete Road Making Properties of Minnesota 

Stone and Gravel ; by Chas. F. Shoop. 

Studies in Eng. No. 2, University of Minnesota, 1915. 
Some Comparative Tests of Wearing Qualities of Paving Brick and Con- 
crete ; by F. L. Roman. 

Municipal Engineering, Aug., 1916. 
Tests of Concrete Road Aggregates; by J. P. Nash. 

Proc. Am. Soc. Testing Materials, Part II, 1917. 



28 



Structural Materials Research Laboratory 



Effect of Time of Mixing on the Strength and Wear of Concrete; by 

Duff A. Abrams. 

Proc. Am. Concrete Institute, 1918. 
Wear Resisting Values of Various Aggregates for Concrete Roads; by 

H. S. Mattimore. 

Engineering News-Record, May 2, 1918. 

Abrasion Tests of Stone, Etc. 

The original work of Deval in developing the abrasion test for crushed 
rocks for use in macadam road construction is described in Annales 
des Ponts et Chaussees, 1879, and Bulletin du Ministere des Travaux 
Publics, 1881. 



CONSISTENCY 
*100i 




vSand 2d, 



Sand 2/ i 



Sav&4m<i 



S A N D 4 MO 
CR. STONE 



LLLLL1IIU 





JoJJlLlLL 

LLLLIL 




Fig. 17— Side View of Wear Blocks after Test. 

The effect of storage condition on wear is clearly shown. 
For the early history of tests of road materials in the United States, see 

The U. S. Road Materials Laboratory; by L. W. Page and A. S. 

Cushman. 

Proc. Am. Soc. Testing Materials, 1903. 
For an account of the use of the Talbot-Jones rattler for paving brick 

tests, see Proc. National Brick Manufacturers' Association, 1899, 1900 

and 1901 ; also, Testing of Road Materials; by L. W. Page. 

Bulletin No. 79, U. S. Bureau of Chemistry, 1903. 



Wear and Strength of Concrete 



29 



For a description of the Dorry hardness test for natural rocks, see Bul- 
letins 44, 49 and 347, U. S. Bureau of Public Roads. 

Strength and Wear of Building Stones; by A. Hanisch. 
Mitt. Techn. Gewesbemuscums, 1907. 

For a description of the Deval abrasion test for broken stone, see Stand- 
ards ; Am. Soc. Testing Materials, 1918, p. 623. 

The Sand-blast as an Abrasive Agent for Testing Purposes; by M. Gary. 
Baumatcrialeinkunde, Vol. 10. Table of results in Johnson's Ma- 
terials of Construction. 

Testing Building Materials by the Sand-blast Method; by H. Burchartz. 
Engineering (London), Nov. 30, 1906. 




Savo4..mu 



Sa*<d4 

'"R- STONE 



Fig. 18 — Side View of Blocks after Test. 

The effect of storage condition on wear is clearly shown. 



Note on Appliances for Testing Paving Setts ; by Labordere and Anstett. 

Proc. 6th Cong. Int. Ass'n Testing Materials, 1912, 2nd Section 

Paper XIX. 
Relation between the Tests for the Wearing Qualities of Road-Building 

Rocks; by L. W. Page. 

Proc. Am. Soc. Testing Materials, 1913. 
For a modified form of the Deval abrasion test, see Abrasion Test for 

Gravel Aggregate ; by A. S. Rea. 

Concrete Highway Magazine, June, 1918. 



30 



Structural Materials Research Laboratory 



General Specifications for Materials; Ohio State Highway Depart- 
ment, Columbus. 

For a description of the present standard rattler test of paving brick, see 
Standards; Am. Soc. Testing Materials, 1918, p. 549. 

An Abrasion Test for Stone, Gravel and Similar Aggregate ; by H. H. 
Scofield. 

Proc. Am. Soc. Testing Materials, Part II, 1918. 
(Discussion by H. S. Mattimore) 




CONSISTENCY 
1Z5 



LLLtiniii 

LULU 



Sanb 2d, 



S.«D 21 D. 



Sand 4 Ma 




LLLLLLLLL 








Fig. 19 — Side View of Wear Blocks after Test. 

The effect of storage condition on wear is clearly shown. 

Effect of Consistency of Concrete 

Relative Strength of Wet and Dry Concrete ; by J. W. Sussex. 

Technograph (Univ. of 111.), 1902-3. Also Eng. News, July 16, 1903. 
Strength of Concrete as Affected by Different Percentages of Water; by 

T. L. Doyle and E. R. Justice, Eng. News, July 30, 1903. 
Tests of Concrete; by Geo. W. Rafter. 

Municipal Engineering, Jan., 1903. 
The Consistency 'of Concrete ; by S. E. Thompson. 

Proc. Am. Soc. Testing Materials, 1906. 



Wear and Strength of Concrete 



31 



Excess Water in Cement Mixtures ; by A. B. Pacini and others. 

Concrete-Cement Age, Dec, 1912, page 155. 
Effect of too much Water in Mixing Concrete; by C. J. Robinson. 

Eng. News, May 22, 1913. 
The Experimental Determination of the Effect of Varying the Percentage 

of Water in Concrete; by R. K. Skelton. 

Proc. Connecticut Soc. Civ. Eng., 1914. 
Strength and Other Properties of Concrete as Affected by Materials and 

Methods of Preparation; by R. J. Wig, C. M. Williams, and E. R. 

Gates. 

Technologic Paper No. 58, U. S. Bureau of Standards, 1916.* 



Storv 
Air 4 



Sand 2d. 



Sand 2Jd. 



Sand 4 Ma 



Sand4m 

CR STONE 




LLHXUXl 



Fig. 20— Side View of Wear Blocks after Test. 

The effect of storage condition on wear is clearly shown. 

Effect of Grading of Sands and Consistency of Mix upon the Strength 

of Plain and Reinforced Concrete; by L. N. Edwards. 

Proc. Am. Soc. Testing Materials, Part IT, 1917, p. 301. Also Part II, 

1918, p. 303. 
Tests of Slabs to Determine the Effect of Removing Excess Water; by 

A. N. Johnson. 

Proc. Am. Soc. Testing Materials, Part II, 1917, p. 378. 



32 



Structural Materials Research Laboratory 



Design of Concrete Mixtures ; by Duff A. Abrams. 

Bulletin 1, Structural Materials Research Laboratory, April, 1919. 

Effect of Curing Conditions 

Recommended Practice for Concrete Road and Street Construction. 
Proc. Am. Concrete Institute, 1918. 




Fig. 21 — Side View of Wear Blocks after Test. 

Some of the blocks which were stored for the entire four 
months in air were completely broken up before the end of the 
test run. The blocks, missing from the two lower rows were lost 
before the photograph was taken. 



Seven-Year Tests Showing the Effect of Age and Curing Conditions on 

the Strength of Concrete ; by M. O. Withey, Wisconsin Engineer, 

Feb., 1918. 
Effect of Age and Condition of Storage on the Strength of Concrete; by 

H. F. Gonnerman. 

Proc. Am. Concrete Institute, 1918. 



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